NASA seeks 'Plan B' for planet-hunting probe Kepler

By Matt Smith, CNN

Updated 4:00 PM ET, Thu August 15, 2013

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Photos:Where life might live beyond Earth

The Kepler mission has discovered 1,284 new planets. Of these newly discovered planets, nine orbit in the habitable zone of their star and nearly 550 are possibly rocky planets roughly around the same size as Earth.

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Photos:Where life might live beyond Earth

This artist's impression shows an imagined view from the surface one of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO's La Silla Observatory. Given the proximity of the dwarf star, the rosy sun would appear very large in the sky.

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Photos:Where life might live beyond Earth

On Thursday, July 23, NASA announced the discovery of Kepler-452b, "Earth's bigger, older cousin." This artistic concept shows what the planet might look like. Scientists can't tell yet whether Kepler-452b has oceans and continents like Earth.

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Photos:Where life might live beyond Earth

Kepler-452b is about 60% larger than Earth, left. It's about 1,400 light-years from Earth in the constellation Cygnus.

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Photos:Where life might live beyond Earth

A team of astronomers announced April 17, 2014, that they discovered the first Earth-size planet orbiting a star in the "habitable zone": the distance from a star where liquid water might pool on the surface. That doesn't mean this planet has life on it, says Thomas Barclay, a scientist at the Bay Area Environmental Research Institute at Ames and a co-author of a paper on the planet, called Kepler-186f. He says the planet can be thought of as an "Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth." The planet was discovered by NASA's Kepler Space Telescope. It's about 500 light-years from Earth in the constellation Cygnus. The picture above is an artist's concept of what it might look like.

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Photos:Where life might live beyond Earth

Scientists announced in June 2013 that three planets orbiting star Gliese 667C could be habitable. This is an artist's impression of the view from one of those planets, looking toward the parent star in the center. The other two stars in the system are visible to the right.

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Photos:Where life might live beyond Earth

This diagram shows the planets thought to orbit star Gliese 667C, where c, f and e appear to be capable of having liquid water. The relative sizes, but not relative separations, are shown to scale.

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Photos:Where life might live beyond Earth

This diagram lines up planets recently discovered by Kepler in terms of their sizes, compared with Earth. Kepler-22b was announced in December 2011; the three Super-Earths were announced April 18, 2013. All of them could potentially host life, but we do not know anything definitive about their compositions or atmosphere.

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Photos:Where life might live beyond Earth

This illustration depicts Kepler-62e, a planet in the habitable zone of a star smaller and cooler than the sun. It is about 1,200 light-years from Earth in the constellation Lyra.

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Photos:Where life might live beyond Earth

This illustration depicts Kepler-62f, a planet in the habitable zone of a star smaller and cooler than the sun, in the same system as Kepler-62e.

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Photos:Where life might live beyond Earth

This diagram compares the planets of our own inner solar system to Kepler-62, a five-planet system about 1,200 light-years from Earth. Kepler-62e and Kepler-62f are thought capable of hosting life.

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Photos:Where life might live beyond Earth

The planet Kepler-69c is about 2,700 light-years from Earth in the constellation Cygnus.

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Photos:Where life might live beyond Earth

This diagram compares the planets of our own inner solar system to Kepler-69, which hosts a planet Kepler-69c that appears to be capable of hosting life, in addition to planet Kepler-69b.

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Photos:Where life might live beyond Earth

This artist's illustration represents the variety of planets being detected by NASA's Kepler spacecraft.

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Story highlights

NASA hopes to find an alternative mission for the planet-hunting probe

Kepler has been sidelined since a control device failed in mid-May

Program has ID'd nearly 3,300 possible planets beyond solar system

So, got any ideas for what to do with a used space telescope?

NASA hopes to find a new job for its planet-hunting Kepler probe after efforts to restore precision control of the orbiting telescope have failed, the space agency announced Thursday.

Kepler has been sidelined since mid-May, after the second of four devices used to aim the spacecraft's telescope gave out. Controllers have been trying to restart at least one of those two devices, known as reaction wheels, since July.

"The wheels are sufficiently damaged that they cannot sustain spacecraft pointing control for any extended period of time," Charlie Sobeck, Kepler's deputy project manager, told reporters Thursday afternoon.

That means Kepler's original science mission -- the search for Earth-like planets far beyond our solar system -- is over, said Paul Hertz, the head of NASA's astrophysics division.

But the space agency is trying to figure out whether it can find other missions that don't require that kind of pinpoint control -- and if so, "whether that science is compelling enough to justify continued investment in Kepler operations," Hertz said.

The roughly $600 million mission has so far confirmed 135 planets and identified nearly 3,500 possible planets. It findings have led scientists to believe that most stars in our galaxy have planets circling them. Two of them -- found about 1,200 light-years away -- are considered the best candidates so far for hosting life.

Controllers have remained in communication with the craft, which is more than 45 million miles from Earth. And since scientists still have more than two years of data to comb through, NASA doesn't consider the mission over, said Bill Borucki, the project's principal scientist.

"We have all this data we have not yet analyzed, and we expect many, many more discoveries," he said.

Kepler needs three of its four reaction wheels to tweak the telescope, which is aimed at a sliver of the cosmos around the Northern Hemisphere constellations Cygnus and Lyra. The No. 2 reaction wheel failed in 2012, while the No. 4 unit quit in May.

In a series of tests that began in mid-July, controllers got both reaction wheels to turn. In early August, they stopped tests on wheel No. 4 after finding high levels of friction, but continued testing the second until encountering the same problem last week, Sobeck said.

Sobeck said the probe can still be aimed using the two remaining reaction wheels, and its thrusters -- just not as finely as it could by reaction wheels alone. The thrusters still have enough fuel remaining to last several years if used carefully, he said.

The probe was launched in 2009 and has already surpassed its three-and-a-half-year minimum expected lifespan.

Borucki said NASA has asked scientists to propose alternatives within a few weeks. The agency will then decide "which of these will be practical and which of these we can do for a reasonable cost."